Process for the removal of polynuclear aromatic compounds from a vapor effluent from a normally gaseous hydrocarbon dehydrogenation reaction zone

Abstract

A process for the removal of trace quantities of polynuclear aromatic compounds from the vapor effluent of a hydrocarbon dehydrogenation zone containing normally gaseous olefinic hydrocarbons, trace mononuclear aromatic compounds and trace polynuclear aromatic compounds by cooling the vapor effluent to condense at least a portion thereof, up to five weight percent, by introducing the resulting cooled stream into a vapor-liquid separator to produce a vapor stream containing normally gaseous olefinic hydrocarbons and having a reduced concentration of polynuclear aromatic compounds and a liquid stream containing mononuclear and polynuclear aromatic compounds and by recovering the vapor stream comprising normally gaseous olefinic hydrocarbons having a reduced concentration of polynuclear aromatic compounds.

What is claimed: 
     
       1. A process for the removal of trace quantities of polynuclear aromatic compounds from the vapor effluent of a hydrocarbon dehydrogenation zone comprising normally gaseous olefinic hydrocarbons, trace mononuclear aromatic compounds and trace polynuclear aromatic compounds which process comprises: (a) cooling substantially all of said vapor effluent to condense at least a portion thereof up to about 5 weight percent;   (b) introducing the resulting cooled stream from step (a) into a vapor-liquid separator to produce a vapor stream comprising normally gaseous olefinic hydrocarbons and having a reduced concentration of polynuclear aromatic compounds and a liquid stream comprising mononuclear and polynuclear aromatic compounds;   (c) separating said liquid stream comprising mononuclear and polynuclear aromatic compounds recovered in step (b) in a separation zone to produce a stream rich in mononuclear aromatic compounds; and   (d) recovering said vapor stream comprising normally gaseous olefinic hydrocarbons having a reduced concentration of polynuclear aromatic compounds.   
     
     
       2. The process of claim 1 wherein said separation zone is a fractionation zone. 
     
     
       3. The process of claim 1 wherein said separation zone is an adsorption zone. 
     
     
       4. The process of claim 1 wherein said normally gaseous olefinic hydrocarbons are selected from the group consisting of ethylene, propylene and butylene. 
     
     
       5. The process of claim 1 wherein said mononuclear aromatic compounds are selected from the group consisting of benzene, toluene and xylene. 
     
     
       6. The process of claim 1 wherein the trace quantities of polynuclear aromatic compounds are present in the vapor effluent of a dehydrogenation zone in an amount from about 50 to about 500 wppm. 
     
     
       7. The process of claim 1 wherein the trace quantities of mononuclear aromatic compounds are present in the vapor effluent of a dehydrogenation zone in an amount from about 100 to about 5000 wppm. 
     
     
       8. The process of claim 1 wherein said stream comprising normally gaseous olefinic hydrocarbons having a reduced concentration of polynuclear aromatic compounds contains less than about 1 wppm polynuclear aromatic compounds.